Chronograph



June 2, 1925.

G. B. VROOM CHRONOGRAPH Filed June 6, 1924 attain,

Patented June 2, 1925.

UNITED STATES GUYSBERT BOGERT VROOM, OF WASHINGTON, DISTRICT OF COLUMBIA.

CHRONOGRAPH.

Application led June 6,

To all 'whom t may conce/m:

Be it known that I, GUYSBERT B. YRooM, a citizen of the United States, residingat .Washingtom District of Columbia, have invented new and useful Improvements` in Chronographs, of which the following is a specification.

This invention relates to improvements 1n chronographs and more particularly to instruments of the above character particularly adapted for indicating simultaneously cross-head displacement and cylinder pressure, for example.

One of the objects of the present invention is to provide a device of the above general character for simultaneously indicating two curves denoting, for example, cross-head displacement and cylinder pressure whereby 4 these curves may be subsequently analyzed with respect to each other to more accurately determine the performance and condition of the apparatus to which it is applied.

A further object of the invention is to provide a simple and practical apparatus of the above character adapted to permit the checking of the displacement of cross-head as actually obtained with empirical valve settings and resulting air, oi steam, or gas pressures against the ideal displacement curve.

A further object is to provide a reliable and eficient apparatus for Calibrating the movement of the cross-head, or piston, for example, which will enable the construction of a table of pressures, to be used for obtaining the desired resultant operation.

vWhile the invention will hereinafter be described with relation to its application of determining the movement of a catapult used in launching aircraft it is, of course, to be understood that it is applicable to `any form or type of power mechanism where cylinder pressure and cross-head movements or the equivalents are desired to be obtained.

Other objects will be in part obvious and in part hereinafter pointed out in connection with the accompanying sheets of drawings. In these drawings Figure 1 is a semidiagrammatic elevational view showing the cylinder and the complete apparatus connected therewith.

Fi ures 2 and 3 illustrate the curves upon the chronograph cards. i

Referring to the drawing in detail1 5 indi- 1924. serial No. 118,405.

cates a cylinder of any desired character provided with a piston 6 and a cross-head 7. The opposite ends of the cylinder are provided with pipes 8 and 10, each provided with a valve 11 and a branch pipe 12 leadmg to-an ordinary pressure mechanism of the well-known Thompson type 13. To briefly describe this well-known mechanism it consists of a cylinder 14. provided with an outwardly extending piston rod 15 connected with an arm 16 pivotally -mounted at 17 and carrying the pencil 18 adapted to coact with the indicator card mounted upon a cylinder 20. This cylinder is driven by means of a series of reduction gears 21 from a motor 22 at a constant rate of speed as distinguished from previous constructions in lwhich the cylinder is rotated as the piston moves outwardly.

To this indicator there is provided an attachment in the form of a slotted arm 23 in which travels a block 24 supporting the pencil and this block is connectedy by means of a rod 25 or the like having a connection at 2G with a link 27 pivoted at 28. This link has a connection 3() with the cross-head 7 whereby as the cross-head moves outwardly to dotted line position the opposite end 26 moves a proportionally less amount or a distance equal to the length of the cylinder 20.

It will thus be seen that the recording cylinder rotating at a constant rate of speed will, when the piston is actuated, have drawn on the indicator card two curves, one by the pencil 18 indicatingcylinder pressures and the other by the pencil 24 indicating piston displacement.

One of these curves is slightly in advance of the other and by advancing the two curves .the desired information regarding the condition and performance of the apparatus may be obtained.

In order to illustrate the uses to which this invention may be applied reference is made to Figure 2 of the drawings.

Since the recording cylinder revolves at a known rate previously determined, the reference line O-X, drawn by the pencil 24 when the instrument is started, represents the time in seconds for one revolution of the recording cylinder of the indicator. When the catapult cross-head makes its stroke, the displacement curve is drawn; point n is the end of the stroke, and the distance Xn is the. total displacement of the cross-head, to the scale determined by the design of the reducing mechanism wmztime for coniplete stroke.

Since argthe instantaneous velocity :it any point may be obtained by drawing a tangent to the displacement time curve at the desired point and multiplying the tangent of the angle this line makes with the axis of time by the proper constant. By repeating this process for a number of points and plotting the values so obtained, a velocity time curve may be obtained whose ordinates will represent the velocity at any instant.

In other words the velocity time curve is obtained from the displacement time curve by graphically differentiating the displacenient curve.

By repeating the process using the new velocity time curve, an acceleration time curve may be obtained, the ordinates of this c urve will represent the acceleration at any time.

Figure 3 shows a complete card obtained on a trial 'of the catapult. Its analysis gives all necessary data regarding the functioning of the valves, such as the time required for valve opening; time required to take up the slack in the cable before the car begins to move; the length of the power stroke; power required toobtain a given average acceleration and final velocity, from which the pressure required for the launching of other weights may be predicted; average acceleration; instantaneous acceleration and velocity.

Referring to Figure 3, the speed of the recording cylinder was regulated to three seconds per revolution. Therefore, the line AB represents three seconds and, since it is 6.3 inches long, 0.1 inches represents 1/21 seconds.

The instrument is started before the catapult is fired, and the two lines AB and CD are drawn by the pencil 18 andthe indicater pencil 24 respectively. These lines are the base lines, or lines of reference, for the displacement and pressure curves respectively. The rotation of the recording cylinder is continuous, and until the catapult is fired the pencils simply move over the lines AB and CD.

At the instant of firing, however, the displacement and pressure curves are drawn, starting from points e and 1. (Fig. 3). The curves will be considered separately.

The pressure curve is klmnoprk, Figure 3. With reference to the base line, which represents atmospheric pressure, the instantaneous pressure can be measured by scale, according to the scale of indicator spring used. Point l shows the maximum pressure; from Z to y the pressure remained constant showing that the length of the line Zy (to the scale 1/10 inch is equal to 1/21 second) is the time required to take up the slack in the cable. From y to m to a to o the pressure falls as the piston moves forward, the exhaust valve opening 'at 0. -The power stroke, therefore, may be referred to the base line CD to find the time required for the stroke, and referred back to the base line of the displacement curve to find the corresponding instant on the displacement curve, and the piston displacement represented by that point. Turning to the displacement curve, it commences at e, following to w to f to y to g to L. The point g represents the maximum travel of the cross-head, to the scale of the reduction as heretofore described. At the point g' the cross-head comes to rest and therefore the pencil 24 draws a straight line igi parallel to AB. The complete displacement curve is therefore efyg, To ,the scale of 1/10 inch equals l/21 second, the time required for the stroke is @A plus z'g. With e and 7c as the starting points of the displacement and pressure curves respectively, and using the above time-displacement scale, corresponding points on the two curves may be foundL (It must be remembered that e corresponds to 3/ in point of time, since the pressure is building up from 7c to Z, and the time ly represents the time required to'take the slack out of the cable before the car begins to move (point e).

To find the instantaneous velocity at any point on the displacement curve, the following procedure is followed in cases where a practical analysis only is required.

Select two points on the base line AB, such that they are .05 inch apart and from these points drop perpcndiculars to the displacement curve. .O5 inch (in the case of the example under discussion) on the base line. represents a time interval of l/LQ of a second. The difference of the length of the perpeiidiculars is equal to the space traversed, or the displacement of the crosshead, in l/42 of a second. Let the difference of the length of the perpeiidiculars, as measured, be represented by S and the time interval (in this case l/42 of a second) by t. Then V, the instantaneous velocity, since the measurable quantities are exceedingly small as compared to the total displacement and elapsed time per stroke (see Kent,

9th Ed. i916, P. 521), is equal to It is obvious that the rate of rotation of the recording cylinder may be selected as commensurate with the rate of operation of the machine to be analyzed in order that the curves may be well defined and that resent, with respect to the time element, a small value of t. In effect, the equation given above, V= is, if the quantities chosen are relatively very small, as they should be in the discretion of the operator,

fv=g The above method is applicable for all practical purposes but does not take into .05 inch is a straight line. Analysis may .thus be expeditiously carried out, to avoid the more laborious method of finding the equation of the displacement curve and analyzing it mathematically.

The average displacement is found from @zi/aar. .The points on the displacement curve representing maximum velocity may be found by drawing the tangent to the curve from hz' as a base line. These points may be referred to the pressure curve by dropping the perpendicular to the base line AB and, having determined the elapsed time from the origin, using the elapsed time to the same scale on the pressure curve baseline CD, dropping the perpendicular to the pressure curve, to find the pressure corresponding to a maximum velocity.

In Figure 3, if a perpendicular is dropped from Z to CD, csztime required for :valve to open and pressure to build up; likewise etz-time required to take up slack of cable; in further `analyzing the curves, it can be shown that point 0 on the pressure curve, at which the pressure is released, corresponds to the point on the displacement curve showing maximum velocity.

It should be noted, in examining Figure 3, that the card differs from the ordinary indicator card in that the rotation of the recording cylinder of the mechanism is continuous, and not reciprocating; and that the curves are not closed curves. The part of the paper containing the space for notes is overlapped when the paper is on the cylinder, and therefore points w and f, m and n, p and r, 71, and z' are identical. y

It will thus be seen that the present invention contemplates a simple and practical apparatus as well as a method of obtaining pressure and displacement curves of reciprocating engines oiV various kinds whereby on subsequentanalysis of these curves the resulting operation of the engine may be easily and quickly ascertained'.

What I claim is 1. In an instrument of the character described, in combination, a cylinder adapted to carry an indicator card, means for driving said cylinder at a constant rate of speed and means for indicating on said card crosshead displacement and cylinder pressures.

2. In an instrument of the character described, in combination, a member adapted to carry an indicator card, means for driving said member at a constant speed, means for simultaneously marking on said card two curves, one of which indicates crosshead displacement and the other of whic indicates cylinder pressure.

3. In an instrument of the character described, in combination, a member adapted to carry an indicator card, means for mov.- ing said indicator card at a constant rate of speed, means adapted to mark on said card a curve indicatin cylinder pressure and separate means a apted to mark on said card in offset relation thereto a curve indicating cross-head displacement whereby said'curves may be analyzed to determine the condition and operation of the machine to be tested.

4. In combination with a pressure displacement engine to be tested, including a cylinder and cross-head, a chronograph card, means -for moving said card at a constant speed, means connected with the interior of the cylinder and actuated by the pressures thereln for recording the pressure upon 'said card during the complete stroke and a second means connected with the cross-head and adapted to indicate upon said card a curve denoting cross-head ,displacement whereby said curves may be subsequently analyzed to determine the performance and condition of the engine tested.

' 5. The herein described method of determining the condition and operation of a pressure actuated device which consists 1n simultaneously recording cross-head displacement and cylinder pressure and analyzing said curves one with respect to the other.

Signed at Washington, District of Columbia, this 24 day of March, 1924.

GUYsBERr BoGER'r vRooM. 

